The invention relates to a tachograph having a cubic housing and a printing device, which has a thermal print head, a feed roller which is driven by a drive mechanism, and a carrier which can be moved out of the housing and is used for reloading a ribbon which forms the stock of printing material, and further having means for locking and unlocking the carrier in its closed position in the housing of the tachograph.
Tachographs which are not designed for the use of record charts as recording media, but rather in which the driving and working time data determined are stored in suitably designed bulk memories, require suitable printing devices for documentation in the form of a visually readable document. These devices have to be arranged inside the tachographs since there is generally not enough space in a driver's cab of a commercial vehicle for the installation of an independent printer which corresponds with the tachograph. If a tachograph of this type is equipped with a printing device which, contrary to the use of plug-in, card-like printing substrates, envisages a printing principle with strip-like or ribbon-like printing material, it is necessary for the printing device in question to be loaded with the stock of printing material and for the starting section of the printing material to be moved into the printing position.
One problem is, however, that tachographs are generally designed as built-in appliances and are therefore fitted with a flush front wall so that access for reloading the stock of printing material is only possible from the front side using a carrier which can be displaced in the manner of a drawer or can be pivoted open/folded open on the front side. In this case, in the area in which a tachograph is used, in which considerable vibration and shock loads occur, the locking and unlocking means assigned to the carrier are of crucial importance.
DE-U 29720521 discloses a tachograph, in which a drawer-like carrier is provided for holding the entire printing device and is assigned a bistable snap-in mechanism. In the event of printing material having to be refilled, the carrier is unlocked by actuation of the front panel of the carrier, which panel serves as a pushbutton, and, when the front panel is released, is displaced into the insertion position. Apart from the outlay and an unreliable performance in respect of security against shocks because of the not inconsiderable mass of the carrier, the bistable snap-in mechanism requires the carrier to be able to be moved in the locked state, in the direction of the rear wall of the housing of the tachograph, which makes sealing of the front panel with respect to the front wall of the tachograph considerably more difficult in the locked state of the carrier.
The same applies to a printing device described in DE-U 29920901, in which a thermal print head is arranged in a fixed position in the housing of the tachograph and the feed roller mounted in the carrier has to be brought into operative connection again with the thermal print head when the carrier is closed after each insertion of a ribbon. In such a printing device, the relatively high press-on force of the thermal print head obstructs the ability of the carrier to move, and so the snap-in mechanism has to be equipped with an extremely strong ejection spring or the carrier has to be pulled out by hand after being unlocked, which, apart from being disadvantageous to handle, requires esthetically unfavorable gripping means to be provided on the front panel of the carrier.